Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $55.44   7.570%   $59.6368   $59.64   $59.65   $59.60  
  Purchase #2 $101.90   4.169%   $106.1482   $106.15   $106.15   $106.10  
  Purchase #3 $221.96   5.853%   $234.9513   $234.95   $234.95   $235.00  
  Purchase #4 $100.55   13.632%   $114.257   $114.26   $114.25   $114.30  
  Purchase #5 $224.81   12.547%   $253.0169   $253.02   $253.00   $253.00  
  Purchase #6 $63.99   9.581%   $70.1209   $70.12   $70.10   $70.10  
  Purchase #7 $159.47   5.608%   $168.4131   $168.41   $168.40   $168.40  
  7 purchase totals = $928.12       $1,006.5442   $1,006.55   $1,006.50   $1,006.50